Production of magnesium



F. J. HANsGlRG PRODUCTION oF MAGNESIUM original Filed May 27, 194e mwm y IN VEN TOR. @www mz By w@ M; w Wm l l Mf/f/eys Oct. 31, 1950 Patented Oct. 31, 1950 PRODUCTION OF MAGNESIUM Fritz J. Hansgirg, deceased, late of Yonkers,N. Y., by Josefine Maria Hansgirg, administratrix, Yonkers, -N. Y., assignor to North Carolina. Magnesium Development Corporation, Asheville, N. C.a corporation of North Carolina Original application May 27, 1946, Serial No. 672,531. Divided and thisl application July 5, 1950, Serial No. 172,142

4 claims. (c1. 75467) ,'This invention relates to the production of metallic magnesium, and has for its general object the provision of novel processes for recovering the metal by reduction from magnesium silicates and related materials.

This application is a division of copending application Serial No. 672,531, filed May 27, 1946.

In my United States Patents Nos. 2,372,571 and 2,379,576, I have described processes for producing metallic magnesium from magnesium silicates either by reduction with calcium carbide or by processes involving a pre-reduction step consisting of reducing the silica contained in the magnesium silicates to silicon by the use of carbon, and this without attacking the magnesium oxide in any considerable degree. These processes also include the subsequent step of employing the silicon thus formed as a reducing agent to eiect the evaporation of magnesium vapors from the materials at elevated temperatures and in vacuum.

The present invention contemplates a process briquets at elevated temperatures and either at r atmospheric pressure or in vacuum. In general, such processes are not economical since aluminum is a quite expensive materialk and the processes of bringing the aluminum and the aluminum alloys into a powdered condition adds additional expense.

The present invention, in its preferred embodiment, contemplates the reduction of magnesium silicates, which presents diierent problems from those encountered in the reduction of magnesium oxides. l

Another novel feature of the invention is the effective combination of reduction by aluminum with the pre-reduction with carbon as described as a preliminary step in my Patent No. 2,379,576; but in this case the amount of carbon used is below that which would be necessary to reduce all of the silica.

Within the broad scope of the present invention, the aluminum may be introduced in solid Cil or liquid form and'mixed with the powdered ore either by stirring vigorously or by injection into a suspension of the powdered ore in an air or gas stream. When solid aluminum is used it is intended to be in the same form as described in my copending application, Serial No. 672,812, led May 28, 1946.

Other objects and features of novelty will be apparent from the following specication when read in connection with the accompanying drawings in which certain embodiments of the invention are illustrated and diagrammed, by way of eiiample.

In the drawings: Y

Figure l is a flow chart illustrating a process in which the magnesium silicate ore is ground Y with lime and then the aluminum stirred in; and

Figure 2 is a ow chart showing the steps in a modified process involving a pre-reduction phase.

In one process within the scope of the present invention, the ores used are magnesium silicates, for example, olivine, serpentine, or similar materials. These silicates are ground to a fine powder of 200 mesh or less, and this powder is heated to a temperature slightly above the melting point of aluminum, but below the temperature at which the aluminum starts to react upon the charge. Into this powder, the necessary amount of aluminum is charged either in solid or liquid form, and the whole mass is stirred vigorously Yin order to coat the particles of the mineral powder thoroughly with a thin layer of aluminum.

After this 'coating process is completed, the mass is charged into a rotating drum where it is cooled below the melting point of aluminum and the resulting granulated mass is discharged from the end of the drum. This granulated mass of material is then charged hot into a retort and pure magnesium vapor is evolved at elevated temperatures and under vacuum conditions, the 'vapors being condensed in the usual well known manner. As a residue, an aluminum silicate is formed.

The above process becomes particularly economioal if scrap aluminum is used as the reducing agent. The great consumption of aluminum during the war, and also after the war, has resulted in a huge supply of scrap aluminum, which is very diicult to use again as primary aluminum alloy. A great amount of labor is Anecessary in order to separate the `aluminum from other metals such as steel, copper, zinc, and magnesium. Those skilled in the art know that the composition of aluminum alloys must be i carefully controlled if they are to show valuable mechanical properties. Therefore secondary aluminum as recovered from scrap is a very inferior material for structural or industrial use, if the selection of the scrap has not -been made very carefully. For use in magnesium reduction as in the present invention, aluminum scrap even in an impure form can be used without any adverse inuences on the operation of the process, so that any tedious selection of material can be avoided.

Any scrap metal available on themarket can be directly used in this method.

The reduction of magnesium .oxide with aluminum proceeds according to :the equation,

But in the present case in which magnesium silicates are used, which generally contain magnesium oxide and silica in the ratio of be-i tween ZMgOSiOz to MgOSiOz and it is thennecessary to balance the equation in such a way that icertain aluminum solicates are formed as residues. ,'For example,'if olivines low in iron are vtaken as a Vstarting material, then the reaction proceeds according to the equation,

In this case the ratio of alumina to silica lin the residue is 2:3. Such. aluminum silicateshave a very highmelting point and at the reaction temperature and in vacuumgall partners of the reaction remain in the solidstate.

The yields can be greatly improved if lime isy added to the mixture, since in this case, ternary compounds of alumina, silica, and calcium oxide are formed. By the addition of lime, it is possible toflower the melting pointof the residue to 4 silicon remains incomplete if the necessary amount of lime is not added. To what extent the aluminum reacts directly with magnesium oxide according to Equation2,or indirectly according to Equations?, and 4 depends upon the temperature of the reaction. When added to magnesium silicates, aluminum already starts to react with considerable speed at a temperature of '850 C., and at such temperature about half reacts directly/with the magnesium oxide contained inthe silicates. The other half is used up by the silica to form silicon or ferrosilicon and ysilicon monoxide.

It is therefore possible to conduct the reduction of magnesium silicates with aluminum in two steps. First, at a temperature of between 850 C.

' and 950 C., about half of the magnesium contemperatures of between l300 C. vand 1400 `C.,

:which means that .at-the reaction ltemperature of between 1000"- C.and l200 C., there already occurs some sintering between 'the alumina, silica, andlime. This sintering process has Vtwo advantages, rst the granulatedmass formed during the rst step of the process, in which yii'nely ground magnesium silicates are treated with molten aluminum shrinks `during the evaporation of the magnesium; and second, the granular mass becomes so much more dense which Vinsures the reaction going to completion, and greatly promotes Ythe evolution of Apure dust-,free :magnesium vapors.

In connection with the processes now Abeing described, `refer-ence *isV made to the chart in Figure lof thevdrawings. kIn this figure vand in Figure 2, the reference characters A Yand-A' represent alternative paths pursued, depending upon whetherfthe aluminumV is mixed in in molten form or not.

However, the'formation of a residue of a lower oxide (SiOz) reacts with aluminum according to v.the equation,

Thissiliconcan1later vvreact with the magnesium oxide according to the equation,

It is Aof no vconsermence to the "reduction capacity `of the `added aluminum, in the ultimate result, if the aluminum'rst reduces the silica to silicon, andthis silicon (or'ferrosilicon if iron is present) later reacts Withimagnesium vapors.

But the reactionbetween magnesiumQXCle and.

tained in the ore can bev recovered. Then the temperature has to be raised to from 1100" C. to 1150D C. at which the other half of the Ina-gnesiumcontained in theV ore is recovered. But the second half of the magnesium, based` on the reductionlwith silicon according to Equation 4, canonly be recovered with a high yield, if lime is present. In this two-step process, initially the necessary amount of l'aluminum is added to the magnesium silicates to reduce the magnesium oxide in the silicates without an addition of lime. This mass is then charged into retorts and about iifty per cent of the magnesium contained in the silicateis recovered at a temperature of between 850 C; and 950 C. To the residue from.v this reaction, the'necessary amount of lime is added, and in the second step, the otherlhalf of the' mag- "The recovery'factor in each separation is about `elevenper cent magnesium from 'the charge,

kwhichiis similar to the results of the ferrosilicondolomite reduction. Theggreat advantage in this case, resides in the fact thatinfabout half ofthe piantthe retorts canine operated at from 850 C.

retorts. Y

It is' also `possible to -car'ry'on the processlin -1 oneV step, by -immediately adding thenecessary vamount of lime 'to the mixture of magnesium silicatesandl aluminum, `an`d to carry on the reduction at 'from 1050 C. to 1150 C., and recover the magnesium simultaneously from' both-reduction' reactions.

YI have found that, in reducing magnesium silicates with aluminum, it is of great advantage to put the magnesium silicates through a pre-reduction step; and this com-prises another embodiment of the invention. In this connection, reference is made to the flow chart in Figure '2 of the drawings. Olivines and serpentines contain iron oxide l,and water in varying amounts 'and both these compounds would react with aluminumrand diminish the reducing agent available for the magnesium oxide reduction. Consequently, Yaccordingto a preferred embodiment of the invention, olivines or serpentines are mixed with carbonaceous material in a quantity suflicient to reduce all of the iron oxide and the water to metallic iron` and hydrogen and carbon monoxide, respectively. To this pre-reduced ore, the molten aluminum is vthen admixed as previously described.

It is also possible to combine the reduction by aluminum with the reduction by silicon described in my Patent No. 2,379,576. However, unlike the procedure in the patented process, the magne- `Sum"silicates"are nrst treated with less carbon than is necessary vto produce the amount of silicon needed for the reduction of the total magnesium oxide'content of the magnesium silicates. In this case the pre-reduction step can be carried out at a lower temperature, and the amount of magnesium oxide which is attacked during the pre-reduction step isfreduced practically to zero.

Such-pre-reduction material, consisting of mag nesium oxide, unreacted silica, andferrosilicon is then treated withY aluminum to form a reaction mixture in which the silicon and the aluminum together act as reducing agents, at the same time forming a residue again consisting of silica and alumina.

For the purpose of obtaining a better reaction, calcined lime may be added. Also, in pursuing this combined method, the charge'should preferably be composed in such a way that in the residue the ratio of aluminaY to silica to lime falls be'- tween the ratios 2:3:3 and 223:6;` l f lf; the'pr'e-reduction of magnesiumI silicates with carbonaceous materialv is carried onwith such amounts of carbon that an incomplete reduction ofthe silica takes place, the carbon is reacted completely and ther pre-'reduced material does not contain anymore free carbon."Y This is of great advantage,- as inthe later reduction re'- action when the magnesium vapors are liberated in vacuum, a side reaction between any `surplus carbon and the silica formed can be avoided.

Silica under the conditions" of high vacuum and temperatures between ll00 C. and 1150 C. in reacting with carbon evolves carbon monoxide along with the magnesium vapors, and this interferes with the proper crystallization of the condensed magnesium. Therefore, the combined processes aord a great improvement in the quality of the condensed magnesium, by first retional' twelveto thirteen partsy of.' magnesium recovered.

3) one'hundedprts of'oiivine ofthe above mentioned Vcomposition@are4 ground, -mixed, or?

Vduced to Vferrcsilicofn.-AH -Toone hundred partsr .offy this pre-reduced material, sixteen parts ofT valuminum lare added together with fortyeiivel parts of lime.` The material is granulated at tern--V p'eratures of between 670' C. and 680 C.,"bri-' quetted and charged in the usual way into `r`e torts which are heated to temperatures of be'- tween l050 C. and 1150" C. under high vacuum conditions. Magnesium vapors are evolved and condensed, and the recovery is between twenty' ve to thirty parts magnesium.

It was also founclthat all of the reactions described above underkExamples'l to 3 inclusive,r can be acceleratedV and the yield improved if there is added to the reaction mixture from be# tween,1% lto 10% of calcium fluoride or aluminum fluoride.

ducing the magnesium silicates with carbon to partly provide the necessary silicon for the magnesium reduction, and later adding aluminum in such amounts as to furnish enough reducing agent to reduce the total magnesium oxide content of the charge.

The following examples illustrate the procedures described above in connection with the present invention.

('1) As the starting material, an olivine containing 48% MgO, 8.5% FeO, and 43% SiOz, is used. One hundred parts of this olivine material are treated with three parts of carbonaceous material containing 85% fixed carbon, as a pre-reduction step. To one hundred parts of the prereduced material and forty parts of calcined lime, twenty-five parts of aluminum are added and thoroughly mixed and granulated at a temperature of from 670 C. to 680 C. The granulated mass is then charged in the conventional way into a retort, and the magnesium evaporated under high vacuum at temperatures from between 1050 C. and ll50 C. From this mixture, twentyiive parts of metallic magnesium are produced, and a residue formed wherein the ratio of alumina to silica to lime corresponds to about 2:3 :4.

(2) To one hundred parts of olivine pretreated as described in Example l, from twentyfive to twenty-seven parts of aluminum scrap are added and the mass intimately mixed at a temperature of from 670 C. to 680 C. The mass is granulated and charged into retorts and treated under high vacuum at a temperature of from 850 C. to 950 C. About twelve to thirteen parts of magnesium are recovered. The residue is Y ground and mixed with forty parts of calcined lime, tableted and charged into retorts main- Various kchanges and modifications may vbe made in the embodiments of the invention illustrated and described herein without departing from the scope of the invention as dened by the following claims.

It will be understood that when magnesium silicate is mentioned in the claims, the compound referred to may include magnesium silicate in a relatively pure form or an ore containing various amounts of iron oxide and other heavy metal oxidesand the like. f

Also, the term aluminum as used in the claims in defining the chief reducing agent, may designate either pure aluminum or aluminum alloys such as may be found in the wide varieties of aluminum scrap now-on the market.

Having thusv described the invention, what is' claimed as new and desired to be secured by Letters Patent is:

v l. A process for producing metallic magnesium from magnesium silicate by reduction with aluminum, which comprises mixing together aluminum scrap larger than granular size and thicker than foil and finely ground magnesium silicate at atmospheric pressure and at a temperature just above the melting point of aluminum but below the temperature at which the aluminum starts to react upon the charge, granulating the resulting mass, charging it into a retort, evacuating the retort and maintaining a temperature therein of -from about 850 C. to about 1l50 C., and so evolving magnesium 'Vapor, and condensing said vapor in solid form in the cooler parts of the retort.

2. A process for producing metallic magnesium from magnesium silicate, which comprises mixing a quantity of magnesium silicate in powder form with aluminum of larger than granular size and thicker than foil, at a temperature just above the melting point of aluminum but below the temperature at which the aluminum starts to react upon the charge, granulating the mixture, subjecting the granulated mixture to heat and vacuum in a retort maintained at a temperature of from about 850 C. to about 950 C., thus evolving a part of the magnesium present as a vapor, condensing the magnesiumwapor thus produced; admi-Xing lime-- portion- `o the magnesium as vaponand condensingfsaidf-portion. A

. 3; AV process for producing ,metauicV mag..

nesium;` from magnesium .silicate which mayv containthe usual smallv quantities of -iron oxide and/-otherheavy metal oxides,` said process cornprising .prereducing the magnesium silicate atv a-1temperature-of from about 1400 C. to about 1600 CxwithV carbonaceousV material .in f such amount that the silica` contained in the vmag- Vnesiumfsilcate ispartly reduced and the carbon completely: -used up inl the reaction, addingto such pre-reducedmaterial a quantity of aluminum as-will provide, together with the silicon andferlosilicon liberated,Y sufcent amount of reducing agents that -aiter subjecting` this mixture to elevated temperatures and kvhigh vacuum-magnesium vapor is evolved in pure form, and' without theevolution of carbon monoxide, as would result from an excess of carbon. remaining from the pre-,reduction step, subjecting the mixture of the pre-reduced material and aluminum to suchv high temperature and to Vacuum conditions so, as -to evolve vmagnesiumvapor, and condensinggsaid vapor. I

4. The processaccording to claim 3 in which,

beforeevolvingthelmagnesium, alimefsupplyingmaterial is also added tol the rpre-reducedmaf, terial in such amount that the residue,A after evaporation of. the magnesium, comprises alumina, silica, and lime (CaO) in a ratio of be, tween 223:3 and 2:316.

J OSEFINE MARIA- HANSGIRG. Admfin-stratrirvv of the-Estate of: F-Tz'tz J. Hams-f gzrg, Deceased.

REFERENCE S CITED The following references Vare 'of recordfin 1 the le=of this patent:

UNITED STATES PATENTS Number Name Date-f,

2,126,825 Seliger Aug, 16,1938 2,179,823 Kemmer Nov. 14,1939 2,214,557 Kirk Sept. 10,1940

20 2,282,241 Peake- May5.1942 2,351,488- Cooper June 13, 1944 2,370,898 Whiton et al Mar. V6, 1945 2,372,571 Hansgirg Mar6 27, 1945 2,374,331 Cooke Apr. 24, 1945 25 2,379,576 Hansgirg July, 1945 2,396,658 Hybinette et al. Mar. 19, 1946 2,399,717 lfirveson` May 7, 1946 FOREIGN PATENTSV 0 Number Countryl Date.

Great Britain Nov. 3; l1932 

1. A PROCESS FOR PRODUCING METALLIC MAGNESIUM FROM MAGNESIUM SILICATE BY REDUCTION WITH ALUMINUM, WHICH COMPRISES MIXING TOGETHER ALUMINUM SCRAP LARGER THAN GRANULAR SIZE AND THICKER THAN FOIL AND FINELY GROUND MAGNESIUM SILICATE AT ATMOSPHERIC PRESSURE AND AT A TEMPERATURE JUST ABOVE THE MELTING POINT OF ALUMINUM BUT BELOW THE TEMPERATURE AT WHICH THE ALUMINUM STARTS TO REACT UPON THE CHARGE, CGANULATING THE RESULTING MASS, CHARGING IT INTO A RETORT, EVACUATING THE RETORT AND MAINTAINING A TEMPERATURE THEREIN OF FROM ABOUT 850*C. TO ABOUT 1150*C., AND SO EVOLVING MAGNESIUM VAPOR, AND CONDENSING SAID VAPOR IN SOLID FORM IN THE COOLER PARTS OF THE RETORT. 